I9I5- ^O- 4- REPORT ON ROCK-SPECIMENS. 25 



cracked and like the feldspars shows undulatory extinction. True cata- 

 clases are not shown. 



In the other group the rocks met with are characterised by the 

 absence of potash-feldspar. The chief constituents are: quartz, plagioclase 

 (labradorite An.53 usually, sometimes bytownite) and biotite. The minor 

 constituents are the same as in the first group: magnetite, zircon and 

 apatite. These gneisses are probably derived from dioritic rocks. The 

 structure is fine-grained, apparently aplitic, with biotite arranged in parallel 

 bands. Possibly the entire structure is secondary. 



Summary. 



The rock-specimens from Mt. Betty contain: (i| granites and |2| fine- 

 grained gneisses and mica-schists with well-marked schistosity. The samples 

 prove that the granite is younger than the gneiss. 



The rock-specimens firom Scott's Nunataks contain: (i) granites, 

 ♦ 2) granite-pegmatites, (3) amphibolites and (4) fine-grained gneisses with 

 prominent schistosity. The granite and the granite-pegmatite are younger 

 than the amphibolite and the gneiss. The relative age of the granite and 

 the granite-pegmatite is not determinable. 



The light gray granite ft-om Mt. Betty with regard to chemical and 

 mineral composition as well as external appearance — as stated above — 

 very closely related to the light gray granite from Scott's Nunataks. At 

 both places the granite is intrusive in a complex of older gneiss-rocks. 



The mica-gneisses and mica-schists fi-om both localities are rather alike 

 in external appearance and mineral composition. From their structure and 

 appearance the gneissic rocks (and amphibolites) seem to belong to a highly 

 metamorphic rock-comp'.ex of great geological age, probably archaean or 

 at least pre-Cambrian. The specimens of gneiss have the appearknce of 

 true archæan rocks. From the close resemblance of the pétrographie 

 character of the rock-specimens collected from the two localities, I should 

 think that the conclusion is justifiable, that the rock-cotuplex from Mt. Betty, 

 S. J'ictoria Land, is the same as the rock-complex from Scott's Xunataks, 

 King Edward I'll Land. The gneisses from both places are probably of 

 pre-Cambrian or archaean age, and the granite, which at both localities is 

 the younger rock intersecting and intruding the gneissic rocks, is the same. 

 Later on some remarks will be given as to the probable age of the granites. 



